@Daredek :
It's something I changed too.
My feeling with multicolor variant and some 5 played was to keep the color 'finished' to clue some safe discard (when it's usefull).
I guess it's too rarely usefull compared to the case where having more choice of color to clue a multicolor play for be good.
But yes, for your question, it mean a playable multicolor.
If all multi and color one have already been played, it's either for pass the turn for the player (either what i explain more down or difficult clue or 8 clues left) or for save your chop one more turn.
If you think it's for save your chop, you really should 'pass your turn' by doing an 'empty clue' if it doesn't cost too much.
@motchouli :
For the 'safe discard' (except for 2 players game for avoid twin chop where it's good), I found it the most usefull with 'bad'/'medium' master players.
Imagine, you have a good game, you have lots of clue, you got a good early game, only r2 is played, one r3 have been discarded, there is about ~15 cards on the deck, the other r3 isn't visible, and both r4 are on the deck or in your hand. All others players chop are useless.
It's your turn. All players except you to discard since there is no clue to give.
Should you discard?
Except with what i call 'good master'***, the answer is no because you could hold r4 in chop (others players can't save a 4 who isn't already discarded), and if the other r4 is at the bottom of the deck, you just lost 1 point by discarding.
Please note I take lots of consideration for having an 'obvious' situation, but there is lots of case where it's more close and so it became a choice who depend of lots of parameters.
*** (where it should be on general the player before the player who hold r5 and/or the players who will have few plays at the last turn, even if the argument i explain later is still a good point if nobody did an 'useless clue' before you)